Current liquid phase, homogeneous, ion-catalyzed technology for hydroquinone by the hydroxylation of phenol (as practiced by Rhone-Poulenc) makes substantial quantities of coproduct pyrocatechol (minimum pyrocatechol:hydroquinone ratios are in the region of 1.5:1). As exemplified in a recent patent, Mobil offer the prospect of a highly selective (99%+) hydroxylation to hydroquinone by the use of their proprietary shape-selective zeolite catalyst (HZSM-5).
In this Review, we show that the Mobil approach would be attractive in situations where outlets for pyrocatechol are severely limited. When significant quantities of pyrocatechol can be profitably sold, the nonselective, ion-catalyzed process becomes more economical. However, the zeolite-catalyzed route appears to be potentially more attractive than the p-diisopropyl benzene route.
By: Satish C. Nirula
